This research is concerned with the joint study of neuroelectric signs of human brain function, as manifested by cerebral event-related potentials recorded from scalp, and psychological signs of cognitive behavior. Long latency positive potentials, referred to as P300 components, reflect endogenous central nervous system activity involved in processing and evaluation of information. P300s may occur at about the time of an absent stimulus when such absence is a relevant event for the subject. These components are referred to as emitted potentials. In contrast with evoked potentials, they do not involve factors that reflect the physical presence of a stimulus. They allow a controlled examination of purely endogenous mental processes. Our objectives are: 1) To investigate the properties of (a) potentials elicited by events which require no response but whose features the subject must, in some way, remember, and (b) stimulus- and response-related P300s (emitted and evoked) elicited by events which require a response from the subject; 2) Using near threshold signal detection paradigms, to study how emitted and evoked P300s depend upon stimulus intensity (2AFC) and the subject's criterion (Yes-No); 3) Examine how (a) inter-trial interval duration and (b) the sequency of prior events affect both emitted and evoked P300s.